Implemented `Cond` conditional

* returns the `CDR` of the first true `CAR` in a given list of pairs
* reimplemented `Apply` base class selection in terms of `Cond`

5 files changed, 95 insertions, 8 deletions

diff --git a/src/conditional/cond.h b/src/conditional/cond.h
new file mode 100644
index 0000000..0c2b1a8
--- /dev/null
+++ b/src/conditional/cond.h
@@ -0,0 +1,29 @@
+#ifndef TYPEASVALUE_SRC_CONDITIONAL_COND_H_
+#define TYPEASVALUE_SRC_CONDITIONAL_COND_H_
+
+#include <type_traits>
+
+#include "list/list.h"
+#include "list/operation/higher/find.h"
+
+namespace tav {
+
+template <typename... Branches>
+class Cond {
+	private:
+		template <typename Pair>
+		using predicate = IsTrue<typename Car<Pair>::type::type>;
+
+	public:
+		typedef typename Cdr<
+			typename Find<
+				predicate,
+				typename List<Branches...>::type
+			>::type
+		>::type type;
+
+};
+
+}
+
+#endif  // TYPEASVALUE_SRC_CONDITIONAL_COND_H_
diff --git a/src/function/apply.h b/src/function/apply.h
index 21364a8..5a2105c 100644
--- a/src/function/apply.h
+++ b/src/function/apply.h
@@ -1,7 +1,8 @@
 #ifndef TYPEASVALUE_SRC_FUNCTION_APPLY_H_
 #define TYPEASVALUE_SRC_FUNCTION_APPLY_H_
 
-#include "conditional/if.h"
+#include "operation/math.h"
+#include "conditional/cond.h"
 
 #include "detail/apply.h"
 
@@ -16,14 +17,23 @@ template <
 	template<typename...> class Function,
 	typename...                 Arguments
 >
-struct Apply : If<
-	(detail::count_placeholders<Arguments...>::type::value > 2),
-	detail::apply_variadic<Function, Arguments...>,
-	typename If<
-		detail::count_placeholders<Arguments...>::type::value == 2,
-		detail::apply_pair<Function, Arguments...>,
+struct Apply : Cond<
+	Pair<
+		GreaterThan<typename detail::count_placeholders<Arguments...>::type,  Size<2>>,
+		detail::apply_variadic<Function, Arguments...>
+	>,
+	Pair<
+		IsEqualValue<typename detail::count_placeholders<Arguments...>::type, Size<2>>,
+		detail::apply_pair<Function, Arguments...>
+	>,
+	Pair<
+		IsEqualValue<typename detail::count_placeholders<Arguments...>::type, Size<1>>,
 		detail::apply_single<Function, Arguments...>
-	>::type
+	>,
+	Pair<
+		Boolean<true>,
+		detail::apply_none<Function, Arguments...>
+	>
 >::type { };
 
 }
diff --git a/src/function/detail/apply.h b/src/function/detail/apply.h
index bf60be1..d9f058a 100644
--- a/src/function/detail/apply.h
+++ b/src/function/detail/apply.h
@@ -46,6 +46,14 @@ template <
 	template<typename...> class Function,
 	typename...                 Arguments
 >
+struct apply_none {
+	using type = Function<Arguments...>;
+};
+
+template <
+	template<typename...> class Function,
+	typename...                 Arguments
+>
 struct apply_variadic {
 	template <typename... Partials>
 	using type = Function<
diff --git a/src/type.h b/src/type.h
index c175c36..15ba2f8 100644
--- a/src/type.h
+++ b/src/type.h
@@ -32,6 +32,9 @@ template <
 >
 using IsEqualValue = Boolean<X::value == Y::value>;
 
+template <typename X>
+using IsTrue = IsEqualValue<X, Boolean<true>>;
+
 }
 
 #endif  // TYPEASVALUE_SRC_TYPE_H_
diff --git a/test.cc b/test.cc
index e89fcb1..db19889 100644
--- a/test.cc
+++ b/test.cc
@@ -233,6 +233,31 @@ static_assert(
 	"(if #f 1 2) != 2"
 );
 
+static_assert(
+	std::is_same<
+		tav::Int<2>,
+		tav::Cond<
+			tav::Pair<tav::IsEqualValue<tav::Int<1>, tav::Int<2>>, tav::Int<1>>,
+			tav::Pair<tav::IsEqualValue<tav::Int<2>, tav::Int<2>>, tav::Int<2>>,
+			tav::Pair<tav::IsEqualValue<tav::Int<3>, tav::Int<2>>, tav::Int<3>>
+		>::type
+	>::value,
+	"(cond ((= 1 2) 1) ((= 2 2) 2) ((= 3 2) 3)) != 2"
+);
+
+static_assert(
+	std::is_same<
+		tav::Int<-1>,
+		tav::Cond<
+			tav::Pair<tav::IsEqualValue<tav::Int<1>, tav::Int<2>>, tav::Int< 1>>,
+			tav::Pair<tav::IsEqualValue<tav::Int<2>, tav::Int<3>>, tav::Int< 2>>,
+			tav::Pair<tav::IsEqualValue<tav::Int<3>, tav::Int<4>>, tav::Int< 3>>,
+			tav::Pair<tav::Boolean<true>,                          tav::Int<-1>>
+		>::type
+	>::value,
+	"(cond ((= 1 2) 1) ((= 2 3) 2) ((= 3 4) 3) (else -1)) != -1"
+);
+
 // cons
 
 static_assert(
@@ -1020,3 +1045,15 @@ static_assert(
 	>::value,
 	"(map (lambda (x) (+ x 10)) (list 0 2 4)) != (list 10 12 14)"
 );
+
+static_assert(
+	std::is_same<
+		tav::Int<42>,
+		tav::Apply<
+			tav::Multiply,
+			tav::Int<21>,
+			tav::Int<2>
+		>::type::type
+	>::value,
+	"(* 21 2) != 42"
+);